Liquid pressure remote control system



Sept. 28, 1943. Q. H. CARLTON LIQUID PRESSURE REMOTE CONTROL SYSTEM 4 Sheets-Sheet 1 Filed July 7, 1942 E w s Sept. 28, 1943. H. CARLTON LIQUID PRESSURE REMOTE CONTROL SYSTEM 1942 4 Sheets-Sheet 2 Filed July 7 m zwrm? Q H C/IRL TON 7' 4m) P '1943 I Q. H. CARLTON 2,330,678

LIQUID PRESSURE REMOTE CONTROL SYSTEM Filed July '7, 1942 4 Sheets-Sheet 3 Patented Sept. 28, 1943 LIQUID PRESSURE REMdTE CONTROL I SYSTE M" Quintin Healey Carlton, Ileamington Spa, England, assignortoAutomotive Products Company Limited, Leamington Spa, England Application July 7,1942, Serial'No. 450,061

. In Great Britain June 17, 1941 12 can. (01. sir-54.5)

This invention relates to a two-pipeline liquid pressure remote control system of the kind in which a transmitter and a receiver coupled by a pair of pipelines each comprise apair of cyl- "inder-and-piston units, the pair of pistons in each case being coupled together mechanically tomove in opposite senses. y

' The object of the invention is to provide an improved means for maintaining the correct phase relation between the transmitter and'receiver and for returning them to the proper phase relation if they should become out of phase.

According to the invention, stops are provided to limit the movement of the pistons in both the transmitter and the receiver, the receiver'pistons being movable against resilient loading beyond their positions defined by the stops, and valves are provided which are adapted to be opened mechanically during such excess movement ofthe pistons to place the cylinders in communication with a reservoir. f

According to one aspect of the invention, valves controlling communication between the receiver cylinders and a reservoir are opened only when the respective pistons reach one end of their strokes, resilient stops being provided to resist movement of the pistons to a position in which the valves are opened and further stops. being provided in the transmitterunit which are engaged by the transmitter pistons simultaneously with the engagement of the stops in the receiver unit by the receiver pistons solong as the 'two units are in phase, the resilience of the receiver stops enabling the pistons inthe receiver to be forced beyond their normal stopped position when a receiver piston engages its stop before the corresponding transmitter piston due to loss of phase between the units, thereby openingone of the valves to connect the appropriate receiver cylinder to the reservoir and'permit liquid to escape until the transmitter stop is also engaged.

The valves may be mounted in the pistons to control passages extending through the said pistons, and non-return valves may be provided to permit liquid to enter the pipelines from a reservoir. The valves in the pistons may be operated by members projecting axially from the pistons and adapted to engage with abutme'nts in the cylinders. The receiver unit may comprise a pair of coaxial cylinders mounted on opposite" sides of a central body, a common piston element carrying the pistons in both cylinders and 'mean'sfor element into angular movement of a shaft carconverting longitudinal movement of the piston I riedin the body. The central body may constitute a reservoir for liquid.

The valves inthe pistons are'preferably maintained seated by springs and are connected to rods projecting into the cylinders, the said rods being provided with heads adapted to engage with stops in the cylinders when the pistons are retracted to a predetermined position so that further retraction of the pistons opens the valves.

Th'er'eceiver' cylinders may be arranged side by side," the pistons therein being connected by a rocking arm. The transmitter and receiver units may be substantially identical, the transmitter unit being provided with locking means for holding the pistons in a position in which the valve "in one of the pistons is open,

The invention is hereinafter described with "reference to the accompanying drawings, in which:

Figure '1 "shows the transmitter and receiver 'units of one form of liquid pressure remote control system according to the invention, one half of each unit being shown in section; i

Q Figure 2 is a similar but somewhat diagrammatic illustration of another form of liquid pressure remote control system according to the inventi'on; and

Figure 3 is a view of the receiver unit shown in Figure 2, showing the position of the parts when the valve connecting one of the cylinders to the reservoir is open.

Referring to Figure 1," the liquid pressure remote control system comprises the transmitter unit A and the receiver' unit B, the two being connected by pipelines C and D., The transmitter and receiver units are substantially similar in construction, each comprising a generally rectangular box-like central body, ID from which extendin opposite directions two coaxial cylinders secured against longitudinal movement by wires II inserted into mating grooves in the 'cylinders and the bosses I2 in which they are mounted, the ends of the wires being attached to bolts l3to lockthem in place. Heads M are similarly attached tothe cylinders, and are formed with suitable bosses I5 to receive the bolts l6 of banjo connections I! for the pipelines C and D.

The cylinders of the transmitter unit, indicated Tby references I8 and 2| on the drawing, are connected respectively by the pipes C and D to the cylinders 22 and 23 of there ceiver. The piston elements of the transmitter and receiver, indifcated respectively by-the references 24 and 25 are double ended, each having a head 26 provided With a sealing cup 21 in each of the two cylinders I ,end of the piston element.

of the unit in which it is mounted. Each piston element is formed with rack teeth 28 between its two heads, these teeth meshing with a pinion 3! on a shaft 32 journalled in the body Ill. The piston. elements are supported against bending by 5 rollers 33 mounted in lugs 34 carried by cover members 35 closing lopenings in the. lowerlparts of the bodies of the transmitter and receiver'units'.

Referring now particularly to the transmitter at one end of the piston to engage the corresponding abutment 56, thus moving the rods 2-9 relatively to the piston element and engaging the shoulder on the other rod (18 with the end'of the valve member 5 at the remote end of the piston element to open the valve.

This: form of remote: control system operates in=the*followingmanner; Solong as the transmitter and receiver units remain in phase, the

the piston heads 26 are solid, and flow of liquid lU- stops 38 and ii! on the transmitter and receiver past them is prevented by the-pups 2'1: The shaft 32 carries a hand-lever 35 on opposite;

sides of which are formed two bosses such as that shown at 3'! to received rigid? stop members 38. cooperating with abutments 4i on'thebo'dy' IE! to limit the movement of the hand-lever 36', and thus limit the movementof the element 24. In the receiver unit B, the piston head's illi are formed with axially-extending holes, and thev piston unit itself is bored through to form a pas- 2o sage-:42: A valve seat 43 is formed in-eachpiston head, on which seats the head -Moi a valv'e membertfivurgedron totheseat by a: spring 46. The valve. member 45 is hollow,.andi through-it extends-the reducedfend 4! ofaro'd 48 1yingin the-passage inthe pistonzelem'ent' and abut ting at the centre of thelatteri against-a similar rod-148 associated with :the valve at the: other A seal 49 provides a fluid-tight joint between thevalve member 45 .3 and'the reduced portion of therod. There dueed 1 portions" M of I the rod. 48- terminate just inwards'of the ends-of the valve members-45, theqarrangement being such. that when both valves are'seatedithere is a verysmall clear-135 ance between the inner end of each valve memberand' the shoulder '5! formed by the change" in diameter of the correspondingvalve rod. The interior of the body Hlof there- .ceiverunit forms a reservoir; for liquid, being provided with l a. filler cap 52-. .A' passage 53 connects theinnerside ofthe valve -to this reservoir, and;,a; channel 54 formed on. the survface of the piston, leads to apertures 55 in the piston head: behind the cup 21. Thecup 211s sumcientlyflexible to col-lapse in the eventof the pressure in the cylinder falling, belowthat inL-the. reservoir, andso allow liquidzto flow into the cylinder. In the: head of each'of: thereoeiver cylindersZZ and-23 is mounted an ad- 50 justable abutment 56 with which the endof one .of the rods 48. isadapted. toengagewhenthe piston reaches a-suitable position in the cylinder. Thershaft 32- carrying the pinion-3l in thereoeiver unit has mounted on itexternallyof the .55 body an arm. 5 lhby which. the. receiveris connected to. the member. to be operated,..andon opposite. sides of the arm 51 ardfomied two hollowbosses 58. in. each of whichis mounted aspring-loaded stop 6'! adaptedto engage .with 60 an abutment. 62f on. the. body. The springs 63 of. the stops. 6] are of considerable strength so that an appreciable effort is requiredito corn press them. 1

The stops 6'! andfl butments fi2'aresopositioned a 65 that the angular movement of'the'a-rm 5-! availablewithout compressing the stop springs -63 is equal to :thetot'al angular movement of the transmitter hand-lever 3S; and the abutments 56in thereceiver cylinders 22 and 126. areso positioned that, so long as this-angular movementisnot exceeded, they do not. oomeinto contact with the rods 4543. A greaternmovement of the reoeiver arm 51,..however, which ispermitted by the springs--- 63;". immediately; allows the rod 48 what above. atmospheric pressure.

ment's 55-; and the valves 45 remain closed. The

circuitthusremains closed, except that, should contraction-of liquid in the pipelines occur, liquid can flow thereinto past the cups 2'! on the receiver pistons. Should the units become out of' pliase,"due to leakage or unequal expansion orcontraction. of-the liquid on the two sides, the stop 6'! onthe receiver unit will, when the control-is moved to one extreme position, engage its abutment 62 before the corresponding stop 38 on the. transmitter unit engages its abutment 4|. ltthezoperator then exerts an increased pressure on the hand-lever 36, the spring 63 of the stop 61 will be compressed,- and the piston element 25. of; the receiver. unit 1 will be moved further along-'- the cylinder, with theresult that one of therrods 93 engages with an abutrnent 53, and one of the valves ieis opened to allow the excess-liquid to escapeIfrQ-mthe pipeline. Taking fa-specific.examplaitemaybe assumed that there islaniexcess oflliqhid} inv the right-hand side oflthe system; thatCi's cylinders 2i and 23 and ,pipelineD, and too little liquid in the left-hand side. 'If'thehand-lever 3Eii'smovedin a counterclockwise, direction, it is evident thatstop 6! will engage abutment 6? before the stop on the left-liandside of lever corresponding to stop 38v engages its abutment corresponding ,to M. An ih'creased pressure eXerted'on the lever 36 willcompress the spring 63', and allow the piston elemen't' 25 tomove slightly further to the left,'.th'e .rod 48' at the left-hand side of the drawing engaging the stop 56, and causing the shoulder ofthe right-hand rod 48 to be brought upagainstflthefend of the corresponding valve member 45', to open that valve, allowing the liquidtoes'capefrom the right hand side of the sysindenZZ to fill the space created in that side of" the system by the movement of the piston unit 24: The pressure inthe right-hand side of the'-system'- is now at some relatively high figure dependent game spring 63, and the pressure'pn'the' left-hand side is substantially atmosphe-ric; but the release of the hand-lever 38 .allows this pressure to be. transmitted through theiitransmitter piston to the left-hand side of th'exsystem; leaving both sidesat a pressure some- The clearance. between the shoulders on the rods 48 and the: valvemembers 45 and the additional movementnecessary to bring the rods d8 into con- .taotwith the abutments 56 after the stops 6| have engagethe abutments 62 are both ex- ;tremelyismall, for example of the order of onethousandthotan inch; and, therefore, the movement of the piston element after the stop BI is engaged, and before the valve begins to open is almost infinitesimal. The recovery of the spring 63 when the hand-lever is released mustof course move the receiver piston element the amount of this additional movement, and the transmitter piston element will be correspondingly moved, thus throwing the control very slightly out of phase. With a pitch circle diameter of four inches for the pinion 3i, and'a total lost movement before the valvebegins to open of twothousandths of an inch, the control would be out -of phase by an angle of the order of one-twentieth of a degree-which is negligible.

In the hydraulic remote control system shown in Figures 2 and 3, the transmitter and receiver units A and B are again connected by pipelines C and D, and are identical in form. Each unit comprises a body 64 from which project two cylinders surrounded for a part of their length by a reservoir 65. ,In each cylinder is mounted a piston 66, and the pistons in each unit are conn'ected by pivoted links 61 to a rocking arm 68 secured to a shaft H passing through the body 6 3. The cylinders of the transmitter unit are numbered respectivel 12 and i3, and the cylinders of the receiver unit are numbered 14 and 15 respectively, the cylinders l2 and I5 being connected one to the other by the pipeline C, whilst the cylinders 13 and Mare similarly connected vby the pipeline D. Each of the cylinders T2 to '15 has its upper portion formed integral with the body 64, and its lower portion, which is of slightly smaller diameter, is integral with the reservoir The lower end of the upper part of each cylinder fits into an enlargement 16 of the upper end of the lower part, and serves to retain in the said enlargement a' sealing ring 11 forming a seal for the piston. The lower end of the upper part of the cylinder is slotted as at 18 to admit liquid from the reservoir' to the part of the cylinder above the seal Tl. Another seal 8| mounted in a groove at the upper end of the piston, which is enlarged to fit in the upper part of the cylinder,

whilst the lower part is a sliding fit in the lower part of the cylinder. There is thus provided an annular space around the piston which is in constant communication with the reservoir 65 by way of the slots 18, and this space is connected by diametral passages 82 in the piston to a longitudinal passage 83 therein leading into a cavity 86. in the lower end of the piston. In the cavity 84 is a valve member 85 adapted'to seat in the mouth of the passage 83, the valve member 85 being guided by a stem 86 sliding in the passage 8.3, and having radial ports in the, stem 86 just above its seating face to connect with a longitudinal passage 3'! through the stem. The passage Sl is closed at its lower end by a springloaded non-return valve 88. The valve member 85 is urged on to its seatby a spring at taking its abutment on an annular wall 92 partially closing the cavity 84, and from the valve member extends a stem 93 terminating in a head 94. ;The head 94 lies in the bore of .a hollow adjustable closure plug 95 at the lower end of the cylinder, the upper end of the plug 95 having a restricted opening 96 through which the head 94 cannot pass. It will be seen that when the piston rises 'to a position in which the head}! is stopped by the restricted opening 96 the valve member 85 will'be pulled'off its seat. Figure 3 shows the receiver unit B with the valve 85 of the piston 66 opened. The movement of the pistons of both the transmitter and receiverunits is limited by stops 91 mounted in the bodies 64 of the respectiveunits, the stops cooperating with abutments or lugs 98 formed on the links 61. The stops comprise plungers slidable in adjustable tubular housing Ifll screwed into the body 64, and are loaded by strong springs 192. The stops are set so that, when the control is in phase, one stop in the transmitter unit and one stop in the receiver unit are engaged simultaneously, and such engagement takes place before the heads 94 on the stems 93 of the corresponding pistons are stopped by the restricted openings 96, the clearance at the said heads 94 when the stops 9'! engage being of the order of one-thousandth of an inch.

The reservoirs 65 on the transmitter and receiver units are provided with filler plugs I03 and drain plugs m4. On the shaft H of the transmitter unit A is mounted a hand-lever I05, and

' on the shaft ll of the receiver unit B is mounted an arm N36 for coupling the control to the member which it is to operate. passing through holes in a pair of lugs J03 and through a corresponding hole I09 in the handlever I65, are provided for holding the lever I05 in a position in which the valve 85 of the piston in the cylinder 13 is held open, for a purposeto be described below.

As in the control shown in Figure 1, the system remains closed so long as it is not operated beyond the range limited by the spring-loaded stops 91,

except that liquid can enter from the two reservoirs 65 through the valves 88 to make up for any loss. Whilst the system remains in phase the stops 9! in the transmitter and receiver are engaged simultaneously at either end of the stroke. In the event of loss of phase taking place, the receiver stop 91 at one end of the stroke will come into engagement before the corresponding transmitter stop, and continued pressure on the transmitter hand-lever I35 then causes compression of the spring N2 of the receiver stop, bringing the head 96 on the stem 93 of the appropriate valve 85 up against the end of the restriction 96. and opening the valve 85, to allow the transmitter movement to be continued until the transmitter stop 91' also comes into engagement with its abutment. Figure .3 shows the receiver unit B with the valve 35 of the piston in the cylinder 15 open, the stop ii! on the right-hand side of theunit being forced back against its spring N32 to a low opening of the valvea The clearance at the head 94- has been exaggerated in Figures 2 and. 3. with the result that the stop 91 has required to move an appreciable distance to open the valve, but in practice the clearance would be of the order of one-thousandth of an inch, and the movement of the stop would be correspondingly small. As in the previous case, the return of the stop to its normal position when the handlever M5 was released would involve such a small movement as to be negligible.

If the control is left unused for any considerable length of time, thevariations of temperature to which it is subjectedare liable eventually to build up an excessive pressure in the system, I

which is unable to escape, and may, therefore, do some damage. To avoid this, provision is made for leaving the system in a condition in which the pipelines are open to the reservoirs or are able to be so opened automatically in the event of a rise of pressure. For example, the hand-lever H35 in Figure 2 may be moved over until the stop 91 onthe right of the transmitter is forced back against its spring and the valve 85 of the piston Means, such as a pin 7 strokes. pressure in the control is lost each time an end held-= in: this position by a; pin passed' through the ing position also forces-backthe stop 91- on the right-hand side of the receiver, and opens the valve 85 of thepiston in the cylinder 15. Liquid escapes fromthepipeline C, until the valve 85 .iust, closes, but the head 94- remains in contact Withtheend of the restriction fidand any subsequent increase in pressure in the pipeline C will re-open the. valve, and suchpressure will be relieved; Thus, no pressure can be built up in either side of the system; 1

It: has hitherto been usual, in liquid pressure" remote control systems. of the kind herein described, to arrangev for the opening ofvalves connecting the system to the reservoir whenever the pistons reached the ends of their With that arrangement the working .unittends always to lag slightly behind the transmitter, and accurate phasing of. the transmitter and receiver cannot be obtained. With the present invention, movement of the control within itsnormal range takes place without any opening, of the valves, so that theworking pressure is, never released, and re-phasing is efiected' by movement beyond the normal range, the valves opening against a resilient resistance which'reacts on the liquid and maintains it under pressure even when the excess liquid has escaped.

, It' may be found possible, in controlsaccordin'g to' this invention, to omit'the spring-loaded stopsj illustrated in the drawings, and to provide solid stops attached directly to the body of the transmitter or receiver unit, sufficient movement of: the'stops for the purposes required being permittedfby the resilience of the stops themselves or the parts to which they are attached. The

stopsfor the receiver unit may be provided on the member which it operates instead of on the receiver itself. s

It will be understood that the arrangement shown in- Figure 1 may be provided with valves in the transmitter pistons, and spring-loaded stops fil on'the transmitter, so that the system may be opened for breathing as described with reference to Figures 2 and 3. Similarly, the valves and spring-loaded stops may be omitted from the transmitter in the arrangement shown in Figures 2' and 3. What I claim is:- v

l. A two-pipe-line liquid pressure remote control system comprising a transmitter unit a receiver unit, a pair of cylinders in each unit, pistons in the cylinders, coupling means between the pistons of each unit to-produce simultaneous movement of said pistons in opposite senses, two pipe lines each connecting one cylinder of the transmitter unit to one cylinder of the receiver unit, stops limiting the movement ofthe pistonsinv both the transmitter and the receiver units, resilient means supporting the stopsfor the receiver pistons, and a reservoir, a valve adapted to at times connect each of the cylinders in said. receiver unit to the reservoir,

and means other than said stops to open either of said valves when the piston in the cylinder which. that valve connects to the reservoir is moved beyond the position defined by its stop.

' in the; cylinder (3- opened; the'hand-lever-being 2; A tWo-pipe-line liquid pressure remote con:- trol; system comprising a transmitter unit and a receiver unit, a pair of cylinders in each unit, pistons in the cylinders, coupling means between the pistonsof each unit to produce simultaneous movement'of said pistons in opposite senses, two pipe-lines each connecting one cylinder of the transmitter unit to one cylinder of the receiver unit, stopslimiting the'movement of the pistons in both the transmitter and the receiver units, resilient means supporting the stops for the receiver pistons, a reservoir, a passage through each receiver piston providing a connection between the cylinder in which said piston is .mountedand the reservoir, a valve in said passage adapted to at times connect the cylinder to the reservoir, and means other than said stops to open either of said valves when the piston in the cylinder which that valve connects to the reservoir is moved beyond the position defined by its stop.

3. A two-pipc-line liquid pressure remote control system comprising a transmitter unit and a receiver unit, a pair of cylinders in each unit, pistons in the cylinders, coupling means between the pistons of each unit to produce simultaneous movement of saidpistons in opposite senses, two pipe-lines each connecting one cylinder of the transmitter unit to one cylinder of the receiver unit, stops limiting the movement of the pistons in both the transmitter and the receiver units, resilient means supporting the stops for the receiver pistons, a reservoir, me.- chanically actuated valves each adapted to at times connect one of the cylinders of the receiver unit to the reservoir, means other than said stops for actuating either .of said valves when the iston in the cylinder which that valve connects to the reservoir is moved beyond the position defined by its stop, and non-return valves also ,controlling communication between said receiver. cylinders andsaidreservoir and permitting fiow of liquid. only from said reservoir to said receiver cylinders,

4. A two-pipe-line liquid pressure remote control system comprising a transmitter unit and a receiver unit, a pair of cylinders in each unit,

.pistons in the cylinders, coupling means between the pistons of each unit to produce simultaneous movement of said pistons in opposite senses, twopipe-lines each connecting one cylsaid valves, and abutments in said receiver cylinders other than said stops adapted to engage the operating means of a valve when the piston in the cylinder which that valve connects to the reservoir is moved beyond the position defined by its stop, to open the said Valve.

5. A'two-pipe-line liquid pressure remote control system comprising a transmitter unit and a receiver unit, a pair of cylinders in each unit, pistons in thecylinders, coupling means between the pistons of each unit to produce simultaneous movement of said pistons in opposite senses, two pipe-lines each connecting one cylinder of the transmitter unit to one cylinderof the receiver unit.

a reservoina receiver unit comprising a pair of coaxial cylinders, a central body on opposite sides of which said cylinders are mounted, a common piston element constituting the pistons in both cylinders, a shaft rotationallymounted in said body, means for Converting longitudinal movement of said piston element into rotational movement of said shaft, stops limiting the normal travel of said piston element in both directions, resilient means for supporting saidstops, valves adapted to at times connect each of said co-axial cylinders to the reservoir, and means other than said stops to open one of said valves when the piston element is moved beyond either extreme position defined by the stops, and a transmitter unit providedwith stops to permita travel of the pistons therein corresponding exactly tothe normal travel ofv the receiver pistonsdefined by the resilient stops.

6. In a two-pipe-line liquid pressure remote control system comprising a transmitter unit and a receiver unit, a pair of cylinders ineach unit,- pistons in the cylinders, coupling means between thepistons of each unit to produce simultaneous movement of said pistons in opposite senses, two pipe-lines each connecting one cylinder of the transmitter unit to one cylinder of the receiver unit, a receiver unit comprising a pair of co-axial cylinders a central body on opposite sides of which said cylinders are mounted, said body forming a reservoir, a common piston element constituting the pistons in both cylinders, stops limiting the normal travel of said piston element in both directions, resilient means for supporting said stops, valves adapted to at times connect each of said co-axial cylinders to the reservoir, and means other than said stops to open one of said valves when the piston element is moved beyond either extreme position defined by the stops, and a transmitter unit provided with stops to permit a travel of the pistons therein corresponding exactly to the normal travel of the receiver pistons defined by the resilient stops.

7. A two-pipe-line liquid pressure remote control system comprising a transmitter unit and a receiver unit, a pair of cylinders in each unit, pistons in the cylinders, coupling means between the pistons of each unit to produce simultaneous movement of said pistons in opposite senses, two pipe-lines each connecting one cylinder of the transmitter unit to one cylinder of the receiverunit, stops limiting the movement of the pistons 3 in both the transmitter and the receiver units,

and resilient means supporting the stops for the receiver pistons, said receiver unit comprising a pair of co-axial cylinders, a central body on opposite sides of which said cylinders are mounted, said body forming a reservoir, a common piston element constituting the pistons in both cylinders, passages in said piston element connecting each of said cylinders to said reservoir, a valve seat in each said passage co-aXial with said piston, a valve element co-operating with each said seat, rod means extending slidably through said piston element and having reduced end portions extending through said valve elements to project receiver unit, a pair of cylinders in each unit, pistons in the cylinders, ,couplingmeans between the pistons of each unit toproduce simultaneous movement of said pistons in opposite senses, two pipe-lines each connecting one cylinder of the transmitter unit to one cylinder of the receiver unit, stops limiting the movement of the pistons in boththe transmitter and the receiver units, resilient means supportin the stops for the receiver pistons, a reservoir, a passage through each receiver piston providing aconnection between the cylinder, in which saidpiston is mounted and the reservoir, a valve in said passage adapted to at times connect the cylinder to thereservoir, resilient means tendingto seat, said valves, rods associated with said valves and projecting into the cylinders, and abutment means in said cylinders to engage said rods when the pistons are moved beyond the positions defined by theirstops, to produce opening of the valves. 7

9. A two-pipe-lineliquid pressure remote control system comprising a transmitter unit and a receiver unit, a pair of cylinders in each unit, pistons in thecylinders, coupling means between the pistons of each unit to produce simultaneous movement of said pistons in opposite senses, two pipe-lines each connecting one cylinder of the transmitter unit to one cylinder of the receiver unit, stops limiting the movement of the pistons in both the transmitter and the receiver units, resilient means supporting the stops for the receiver pistons and a reservoir, said receiver unit comprising a pair of cylinders disposed side-byof said rocking arm, a valve adapted to at times connect each of said cylinders to the reservoir, and means other than said stops to open one of said valves when a, piston is moved beyond its extreme position defined by the stop.

10. In a two-pipe-lineliquid pressure remote control system comprising a transmitter unit and a receiver unit each comprising a pair of cylinders, pistons in the cylinders, coupling means between the pistons of each unit to produce simultaneous movement of said pistons in opposite senses, and two pipe-lines each connecting one cylinder of the transmitter unit to one cylinder of the receiver unit; the provision of a receiver unit comprising a body to which the receiver cylinders are attached in side-by-side relation, a rocking arm, rigid links connecting the receiver pistons to opposite ends of the said rocking arm, an abutmenton each said rigid link, resilient stops in said body adapted one to engage each of said abutments and define a normal travel of said beyond the ends of said piston element, abutpistons beyond which they can be moved only by compressing said stops, a reservoir, valves adapted to at times connect each of said receiver cylinders to said reservoir, and means for opening one of said valves when the piston in the receiver cylinder which it connects to the reservoir is moved beyond its normal travel to compress one of the resilient stops, the transmitter unit being provided with stops to permit a travel of the pistons therein corresponding exactly to the normal travel of the receiver pistons defined by the resilient stops.

11. In a two-pipe-line liquid pressure remote control system comprising a transmitter unit and a receiver unit each comprising a pair of cylinders, pistons in the cylinders, coupling means between the pistons of each unit to produce simultaneous movement of said pistons in opposite senses, and two pipe-lines each connecting one cylinder of the transmitter unit to one cylinder of the receiver unit; the provision of a receiver unit comprising a body to which the receiver-cylinders are attached in side-by-side relation, a rocking arm, rigid links connecting the receiver pistons to opposite sides of the said rocking arm, an abutment on each said rigid link, resilient stops in said body comprising plungers, resilient loading means for said plungers, and adjustable tubular housings in which said plungers and loading means are mounted, said stops 'being adapted oneto engage each oi said abutmentsand define a normal travel of said pistons beyond which they can be moved only by compressing said stops, a reservoir, valves adapted to at times connect each of said receiver cylinders to said reservoir,- and means for opening one of said valves when the piston in the receiver cylinder which it connects to the reservoir is moved bey'ond its normal travel to compress one of the resilient stops, the transmitter unit being 'providd with stops to permita travel of the pistons therein corresponding exactly to the normal travel of the'receiver pistons defined by the res'ilient stops.-

I I23In 1a two-:pipe-zline :liquid pressure remote controlsystem'comprisinga transmitter unit and a receiver unit each comprising :a pair of cylinders, "pistons in said cylinders, coupling means between the'pistons of each unittoiproduce simultaneous movement -of :said :pistons in opposite senses, and twozpipe-lines each connecting one cylinder of :the transmitter iinit to one cylinder of the receiver unit; the provision:in *the'transniitter and :receiver units of :stops tlimiting the travel of the pistons therein so that, when the units are in :phase, the corresponding stops the transmitter and receiver 'units are engaged simultaneously, resilient means supporting the said stops, a reservoir in zea chxunit, a; valveadapted to attim'es'connect each;of said cylinders '-to:a reservoir, means other than said stops to open the valvecasso'ciated with each :cylinder when -'the piston in the said cylinder is moved beyond the position defined by its stop to stress 'theresilient supporting means for said stop, and locking means on 'thetransmitterunit .for holding 'a piston 'thereof in a positioniin Whidhthe corresponding valve is open.

Q UINTIN HEALEY CARLTON. 

